Recently, various X-ray imaging systems, which use a CCD (charge coupled device) to take an X-ray image of teeth, etc., of a subject, have been proposed (see, for example, Patent Documents 1 and 2, indicated below). Such an X-ray imaging system has an X-ray irradiating apparatus that irradiates X-rays and an X-ray imaging apparatus that takes an X-ray image obtained by the X-ray irradiation. The X-ray imaging apparatus has an imaging unit, having a CCD for taking the X-ray image, an X-ray detecting unit, for detecting whether or not X-ray irradiation is being performed, and a controlling unit, for drive control of the imaging unit and the X-ray detecting unit.
Here, the X-ray detecting unit is a photodiode, etc., that photoelectrically converts the irradiated X-rays and outputs an X-ray detection signal. The controlling unit detects, on the basis of the X-ray detection signal output from the X-ray detecting unit, a start timing (or, further, an end timing) of an entire X-ray irradiation period for each single time of X-ray imaging (referred to hereinafter simply as the “entire X-ray irradiation period”) and, based on the detected timing, generates a trigger that indicates an imaging start timing (or, further, an imaging end timing). Based on this trigger, the controlling unit performs drive control of the CCD to perform X-ray imaging.    Patent Document 1: Japanese Translation of PCT International Application No. H11-502055    Patent Document 2: Japanese Patent No. 3335350